Generally, an intraocular lens is constituted by an optical portion as a lens body having a high refractive index and a supporting portion capable of securing the optical portion at a predetermined position in an eye. There have been known a three piece type or two piece type intraocular lens wherein the optical portion is prepared separately from the supporting portion which is fixed to the optical portion in the post-treatment, and a one piece type (an integral type) intraocular lens wherein the optical portion is formed integrally with the supporting portion.
In any type of intraocular lens, the optical portion should be formed from material composed of a predetermined polymerization product having excellent optical properties, and the supporting portion should be formed from the material composed of a predetermined polymerization product having properties suitable for supporting the optical portion in an eye, respectively. For this, there has been considered an intraocular lens wherein different polymerization products are used for the optical portion and the supporting portion. For example, an intraocular lens capable of being folded wherein a cut portion in a cornea in inserting operations of the lens is minimized as possible, has been proposed. In the proposed intraocular lens, a polymerization product is used for forming the optical portion which is soft and can be folded, and another polymerization product is used for forming the supporting portion which is hard and has a sufficient rigidity to support the optical portion in an eye. Further, there has been proposed that the optical portion is formed by a transparent material (a first polymerization product) and the supporting portion is formed by a colored material (another polymerization product) so that the position of the supporting portion can easily be confirmed when the intraocular lens is inserted in an eye. For the integral type (i.e., the one piece type) intraocular lens wherein the optical portion is formed integrally with the supporting portion, however, it was difficult to employ straightly such proposed technique, and it was difficult to form only the optical portion by a soft material capable of being folded or to form only the supporting portion by a colored material.
Japanese Unexamined Patent Publication JP-A-4-295353 describes a method for producing an intraocular lens capable of being folded. Namely, a polymerization product for forming a soft optical portion capable of being folded is first formed by polymerization. Then, a round rod-like optical material is formed by processing an outer diameter portion of the polymerization product. The rod-like optical material is placed in a suitable tubular polymerization vessel and another polymerization product, which is different from the first polymerization product, for forming a hard supporting portion is formed by polymerization around the first polymerization product to thereby form an integral composite material. The composite material is processed to obtain a composite-lens-forming blank for forming a single intraocular lens. Then, the composite-lens-forming blank is processed to prepare a one piece type intraocular lens.
In the above-mentioned technique that a predetermined monomer composition for forming the polymerization product for the supporting portion is polymerized around the round rod-like optical material to form the integral composite material, however, it was difficult to keep the round rod-like optical material at the center of the vessel during polymerization. Further, in such composite material in which the supporting-portion-forming material is formed integrally around the optical-portion-forming material due to the polymerization of the monomer composition for supporting portion, a uniform outer diameter could not be obtained due to polymerization shrinkage whereby there causes misalignment between the center of the optical-portion-forming material and the outer diameter of the composite material.
Accordingly, when the ordinary lens processing operations such as shaving, cutting and so on are conducted to the thus obtained composite material to prepare intraocular lenses, the position of connection between the optical portion and the supporting portion varies for individual intraocular lenses and homogeneous products can not be obtained. Further, in a typical intraocular lens in which two supporting portions are symmetrically formed to the optical portion, the two connecting portions between the optical portion and the two supporting portions are deviated from the symmetric position with respect to the center of the optical portion whereby reactions of the supporting portions against an external force are different at both sides of the intraocular lens. The supporting portions of the intraocular lens are adapted to press the capsule in a crystal lens capsule to fix the optical portion to the center of the lens. Accordingly, when the two supporting portions have different reactive forces at the both sides of the optical portion, the function of the intraocular lens is greatly reduced.
Japanese Unexamined Patent Publication JP-A-2-7954 discloses a method for producing an one-piece type intraocular lens having a supporting portion composed of a colored material (a polymerization product). In this method, a rod-like composite material is first produced by forming a colored polymerization product for forming the supporting portion around a transparent optical-portion-forming blank for an optical portion by post-polymerization in the same manner as that disclosed in the above-mentioned JP-A-4-295353 publication. Further, the center of the colored rod-like material of colored polymerization product is perforated by a drill or the like to form an elongated tubular supporting-portion-forming blank. Then, a monomer composition for optical portion is filled in the drilled central opening of the blank followed by polymerizing the monomer composition whereby a composite material in which a transparent polymerization product for forming the optical portion is integrally formed in the central opening is produced. Then, the obtained composite material is cut out to obtain a composite-lens-forming blanks having a predetermined thickness. Each of the blanks is processed to obtain each intraocular lens.
However, the later method wherein the optical portion is formed by the post-polymerization raised several problems. Namely, when the monomer composition for producing the optical portion is filled for polymerization in the central opening of the elongated tubular supporting-portion-forming blank to formed the polymerization product for forming the optical portion, polymerization shrinkage takes place and air bubbles are generated, or an integral structure of the supporting-portion-forming blank and the polymerization product for forming the optical portion at the interface between the inner face of the central opening of the blank and the polymerization product is not sufficiently provided whereby there causes a defect of releasing and so on. Therefore, it was very difficult to obtain a rod-like composite material having a uniform integral structure in its longitudinal direction. In a case of cutting-out a composite-lens-forming blank having a predetermined thickness from such rod-like composite material, it was very difficult to obtain a useful composite-lens-forming blank in which the polymerization product for forming the supporting portion was formed integrally with the polymerization product for forming the optical portion.